Photoelectric encoder and electronic equipment with increased resolution

ABSTRACT

The photoelectric encoder of the present invention has a light-emitting device and light-receiving devices arranged in one direction in a region that light from the light-emitting device can reach. When a moving object that alternately has a light-on portion that produces a state in which light is incident on the light-receiving device and a light-off portion that produces a state in which light is not incident on the light-receiving device passes at a prescribed movement frequency in the one direction, an output of each of the light-receiving devices takes a value corresponding to the incidence or nonincidence of light on the light-receiving device. A logical operating section carries out operation of the logical values expressed by the outputs of the light-receiving devices to form an output signal that has a frequency different from the movement frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Nonprovisional application claims priority under 35 U.S.C. §119(a)on Patent Applications No. 2005-109732 filed in Japan on Apr. 6, 2005,No. 2005-188541 filed in Japan on Jun. 28, 2005 and No. 2005-366734filed in Japan on Dec. 20, 2005, the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to photoelectric encoders. The presentinvention relates, in particular, to, for example, photoelectricencoders of a light transmission type and a light reflection typeemploying a moving object with a plurality of slits formed.

The present invention also relates to electronic equipment provided withsuch a photoelectric encoder. The electronic equipment widely includesprinting machines such as copying machines and printers and FA (FactoryAutomation) equipment such as robots.

As this kind of photoelectric encoder, a light transmission type asshown in FIG. 12A in which a light-emitting section 101 and alight-receiving section 102 are arranged facing each other, and anoutput is obtained by making a moving object 103 that has a plurality ofslits formed pass between the light-emitting section 101 and thelight-receiving section 102, and a light reflection type as shown inFIG. 12B in which a light-emitting section 201 and a light-receivingsection 202 are arranged side by side, and an output is obtained bymaking a moving object 203 that has a plurality of slits formed passthrough positions opposite to the light-emitting section 201 and thelight-receiving section 202 are known.

The photoelectric encoder of the light transmission type often has amoving object 40, which has a plurality of slits X1, X2, . . . at aconstant pitch P in the movement direction and whose slit width is 1/2pitch (i.e., P/2) as schematically shown at the top of FIG. 11 betweenthe light-emitting device and the light-receiving device arranged facingeach other. In the light transmission type, the slits X1, X2, . . .correspond to portions (referred to as a “light-on portion”) that makelight incident on the light-receiving device, and portions Y1, Y2, . . .constructed of a plate material (material of moving object) locatedbetween the slits X1, X2, . . . correspond to portions (referred to as a“light-off portion”) that does not make light incident on thelight-receiving device.

For example, in the device described in JP 3256109, as shown in themiddle of FIG. 11, four photodiodes PD1, PD2, PD3 and PD4 whose width isa half (i.e., P/4) of each slit width are arranged without spacing alongthe direction in which the slits X1, X2, . . . of the moving object 40are arranged, and four signals (assumed to be A+, B−, A− and B+ in asequence) outputted from the photodiodes PD1, PD2, PD3 and PD4 are read.By comparison between A+ and A− and between B+ and B− of these foursignals by respective comparators, two output signals whose phases aremutually different by 90° are obtained.

Moreover, in the device of JP 2001-99684 A, as shown at the bottom ofFIG. 11, four photodiodes 13 a, 13 b, 13 c and 13 d whose width is equal(i.e., P/2) to the slit width are arranged at 3/4 pitch (i.e., 3P/4)along the direction in which the slits X1, X2, . . . of the movingobject 40 are arranged, and four signals (assumed to be A+, B+, A− andB− in a sequence) outputted from the photodiodes 13 a, 13 b, 13 c and 13d are read. By comparison between A+ and A− and between B+ and B− ofthese four signals by respective comparators, two output signals whosephases are mutually different by 90° are obtained.

SUMMARY OF THE INVENTION

In both the prior art examples, the frequency of the output signal isequal to the frequency of the passing of the slits X1, X2, . . . of themoving object 40 through a portion corresponding to a certain photodiode(the frequency referred to as a “movement frequency”). Therefore, minutefrequency changes have conventionally been not able to be read, andthere has been a limitation in improving the resolution during use.

In this case, it can be considered that the frequency of the output ofthe light-receiving device is increased by reducing the slit pitch ofthe moving object in order to improve the resolution. However, if theslit width is narrowed as the slit pitch is reduced, the quantity ofinput light cannot be secured, and this leads to a reduction in the SNratio (signal-to-noise ratio) Moreover, a trouble (crosstalk) that alight-receiving device on which the light that has passed through acertain slit is incident receives diffracted light that has passedthrough the neighbor slit is also considered. An offset between signalsbecomes large, and the characteristics deteriorate.

The same thing can be said for the photoelectric encoder of the lightreflection type, not being limited to the photoelectric encoder of thelight transmission type. However, conversely to the light transmissiontype, the slit corresponds to the light-off portion that makes no lightbe incident on the light-receiving device, and the portion constructedof the plate material between slits (portion that reflects light)corresponds to the light-on portion that makes light incident on thelight-receiving device in the light reflection type.

It is an object of the present invention to provide a photoelectricencoder capable of obtaining an output signal of a frequency higher thanthe movement frequency of the light-on portion regardless of the pitchof the light-on portion (e.g., slit in the light transmission type)provided at the moving object.

Another object is to provide electronic equipment provided with such aphotoelectric encoder.

In order to solve the problem, the photoelectric encoder of the presentinvention comprises:

a light-emitting device; and

a plurality of light-receiving devices which are arranged in onedirection in a region that light from the light-emitting device canreach, wherein,

when a moving object alternately having a light-on portion that producesa state in which the light is incident on the light-receiving device anda light-off portion that produces a state in which the light is notincident on the light-receiving device passes along the one direction ata prescribed movement frequency through a prescribed positioncorresponding to each of the light-receiving devices, an output of eachof the light-receiving devices takes a value corresponding to incidenceor nonincidence of light from the light-emitting device on thelight-receiving device, and further comprises:

a logical operating section for forming an output signal that has afrequency different from the movement frequency through operation oflogical values obtained from the outputs of the light-receiving devices.

In this case, the “movement frequency” means the frequency of thepassing of the light-on portion of the moving object through a positioncorresponding to a certain light-receiving device in a unit time. It isnoted that, when a plurality of light-on portions are provided at themoving object, the individual light-on portions are not distinguished incounting the movement frequency, and the passing of any light-on portionis counted one time.

In the photoelectric encoder of the present invention, the light-onportion and the light-off portion of the moving object alternately passthrough the prescribed position corresponding to each of thelight-receiving devices at a prescribed movement frequency along thedirection in which the light-receiving devices are arranged. Thelight-on portion and the light-off portion produce a state in whichlight from each of the light-emitting device is incident or not incidenton the light-receiving device when passing through the position. Inaccordance with the passing of the light-on portion and the light-offportion of the moving object sequentially through the positionscorresponding to the plurality of light-receiving devices, the outputvalues of the plurality of light-receiving devices sequentially change.Then, the logical operating section carries out operation of the logicalvalues expressed by the outputs of the light-receiving devices to forman output signal that has a frequency different from the movementfrequency. In particular, if the logical operating section forms anoutput signal that has a frequency higher than the movement frequency,the resolution can be improved, and movement information of the movingspeed, the moving direction and so on of the moving object can beobtained more accurately. Moreover, since this is possible even with thepitch of the light-on portions maintained regardless of the pitch of thelight-on portions provided at the moving object, the problems of thereduction in the SN ratio and the crosstalk do not occur. Moreover, ifthe logical operating section forms an output signal that has afrequency lower than the movement frequency when the movement frequencyis comparatively high, it is also possible to prevent waveform collapse.

The actual waveform of the output of each of the light-receiving devicessometimes becomes close to the sine wave rather than a rectangular wavedue to the influence of the diffraction of light. Accordingly, it isdesirable to provide an AD conversion section that forms a digital logicvalue by carrying out AD (analog-to-digital) conversion of the output ofeach of the light-receiving devices. With the arrangement, the output ofeach of the light-receiving devices comes to have a rectangular waveformthat more reliably represents the digital logic value. Furthermore, itis desirable to amplify the output of each of the light-receivingdevices before the AD conversion is carried out.

In the photoelectric encoder of one embodiment, the output signal formedby the logical operating section has a frequency that is an integralmultiple of the movement frequency.

In a stage subsequent to the reception of the photoelectric encoderoutput, it is presumed that an ASIC (Application Specific IntegratedCircuit: Integrated circuit for a specific application) is provided. Inthe photoelectric encoder of the present one embodiment, the frequencyof the output signal formed by the logical operating section is anintegral multiple of the movement frequency. Therefore, taking theoperation of the ASIC into consideration, control can be made smooth,and this is useful.

In the photoelectric encoder of one embodiment, the output signal formedby the logical operating section has a duty ratio different from a dutyratio of the output of each of the light-receiving devices.

In this case, the “duty ratio” means the ratio of a high-level periodand a cycle (=high-level period/cycle) in a cyclic signal that repeats ahigh-level period and a low-level period.

In the photoelectric encoder of the present one embodiment, it ispossible to reduce the consumption current by shortening the ON-statetime of the IC (Integrated Circuit) provided in the stage subsequent tothe photoelectric encoder and prevent waveform collapse when themovement frequency is comparatively high, and this is useful.

In the photoelectric encoder of one embodiment, the light-on portion andthe light-off portion of the moving object have same dimension in theone direction.

In the photoelectric encoder of the present one embodiment, the light-onportion and the light-off portion of the moving object have samedimension in the one direction. Therefore, the same number oflight-receiving devices are easily arranged in the region correspondingto the light-on portion (referred to as a “light-on portioncorresponding region”) and the region corresponding to the light-offportion (referred to as a “light-off portion corresponding region”) inthe one direction. With the arrangement, the background noise can beremoved by taking a difference between the output of the light-receivingdevice placed in the light-on portion corresponding region and theoutput of the light-receiving device placed in the light-off portioncorresponding region. Therefore, the passing of the light-on portion andthe light-off portion of the moving object can be detected with highaccuracy.

In the photoelectric encoder of one embodiment, the logical operatingsection takes an exclusive-OR of logical values expressed by the outputsof the light-receiving devices.

In the photoelectric encoder of the present one embodiment, the logicaloperating section takes an exclusive-OR of the logical values expressedby the outputs of the light-receiving devices. The exclusive-OR has itsoutput changed from logic 1, logic 0, logic 1, . . . as the number ofinputs of logic 1 changes from an odd number, an even number, an oddnumber, . . . Therefore, an output signal of a frequency higher than themovement frequency can easily be formed.

In the photoelectric encoder of one embodiment, the logical operatingsection takes an exclusive-OR (EXOR) of logical values expressed by theoutputs of the light-receiving devices a plurality of times.

In the photoelectric encoder of the present one embodiment, the logicaloperating section takes an exclusive-OR of the logical values expressedby the outputs of the light-receiving devices a plurality of times, andtherefore, an output signal of a frequency higher than the movementfrequency can easily be formed. Moreover, it is possible to increase thefrequency of the output signal and reduce the number of signals incomparison with the case where an exclusive-OR is taken only once, andthis is useful.

In the photoelectric encoder of one embodiment, the logical operatingsection takes an exclusive-OR (EXOR) of logical values expressed by theoutputs of the light-receiving devices and further takes a logicalproduct (AND) or nonconjunction (NAND).

In the photoelectric encoder of the present one embodiment, the logicaloperating section takes an exclusive-OR of the logical values expressedby the outputs of the light-receiving devices to take a logical productor nonconjunction, and therefore, an output signal of a frequency higherthan the movement frequency can easily be formed. Moreover, the logicaloperation becomes simpler than when the exclusive-OR operation isrepeated a plurality of times. Therefore, the number of elements thatconstitute the logical operating section can be reduced.

It is noted that the logical product or nonconjunction may be taken aplurality of times.

In the photoelectric encoder of one embodiment, the logical operatingsection generates a plurality of signals that have a duty ratio of 3/4by taking an exclusive-OR of the logical values expressed by the outputsof the light-receiving devices and, by taking a logical product ornonconjunction of the signals, obtains a signal that has a duty ratio of1/2.

In the photoelectric encoder of the present one embodiment, the logicalproduct or nonconjunction is used in a certain stage of the logicaloperation. Therefore, the logical operation becomes simpler than whenthe exclusive-OR is repeatedly taken a plurality of times. Therefore,the number of elements that constitute the logical operating section canbe reduced.

In the photoelectric encoder of one embodiment, the logical operatingsection comprises an integrated injection logic device and carries outthe operation by using the integrated injection logic device.

In the photoelectric encoder of one embodiment, the integrated injectionlogic (IIL) device is included as a constituent element of the logicaloperating section, and therefore, the logical operating section caneasily be constituted of a bipolar IC. Therefore, it becomes easy tointegrally form the light-receiving device with the logical operatingsection.

In the photoelectric encoder of one embodiment, a plurality of thelight-receiving devices are arranged in the one direction in a light-onportion corresponding region that corresponds to the light-on portion ofthe moving object.

In the photoelectric encoder of the present one embodiment, theplurality of light-receiving devices arranged in the light-on portioncorresponding region output the signals that have mutually differentphases. Therefore, by the logical operating section carrying out theoperation of the logical values expressed by the outputs of thelight-receiving devices, for example, by taking an exclusive-OR (EXOR),an output signal of a frequency higher than the movement frequency caneasily be formed.

In the photoelectric encoder of one embodiment, the plurality oflight-receiving devices arranged in the light-on portion correspondingregion have same dimension and are arranged at a constant pitch in theone direction.

In the photoelectric encoder of the present one embodiment, theplurality of light-receiving devices arranged in the light-on portioncorresponding region output the signals of mutually different phases andsame pulsewidth. With the arrangement, the logical operating section isable to form an output signal that has a frequency higher than themovement frequency and a constant duty ratio.

It is desirable to provide an AD conversion section that forms a digitallogic value by AD (analog-to-digital) conversion of the output of eachof the light-receiving devices as already described. With thearrangement, the output of each of the light-receiving devices comes tohave a rectangular waveform that more securely expresses the digitallogic value. Furthermore, it is desirable to amplify the output of eachof the light-receiving devices before the AD conversion is carried out.

In the photoelectric encoder of one embodiment, the light-receivingdevices located mutually adjacently in the one direction havephotoelectric current output ports that are arranged mutually oppositelyin a direction substantially perpendicular to the one direction.

In order to obtain a frequency higher than the movement frequency, it isdesirable to increase the resolution by reducing the device dimension inthe one direction of each of the light-receiving devices. However, ifthe dimension of each of the light-receiving devices is merely reduced,an area necessary for the output port of the photoelectric current(photoelectric current output port) outputted from each of thelight-receiving devices cannot be secured, and the arrangement becomesdifficult. Accordingly, in the photoelectric encoder of the present oneembodiment, the photoelectric current output ports of the mutuallyadjacent light-receiving devices in the one direction are arranged onthe mutually opposite sides of the array constructed of the plurality oflight-receiving devices in the direction substantially perpendicular tothe one direction. With this arrangement, even when the dimension ofeach of the light-receiving devices is reduced, the area necessary forthe photoelectric current output port of each of the light-receivingdevices can be secured, and the arrangement becomes possible.

In the photoelectric encoder of one embodiment, a plurality of thelight-receiving devices have same dimension and are arranged at commonconstant pitches in the one direction in a light-on portioncorresponding region that corresponds to the light-on portion and alight-off portion corresponding region that corresponds to the light-offportion, respectively, and

the photoelectric encoder comprises a comparing section that makes thelight-receiving devices arranged in the light-on portion correspondingregion and the light-receiving devices arranged in the light-off portioncorresponding region correspond to each other one to one in order ofarrangement in the one direction and takes a difference between outputsof the light-receiving device pair that are made to correspond to eachother one to one, wherein

the logical operating section carries out operation of logical valuesexpressed by differential signals obtained by taking the difference bythe comparing section.

In the photoelectric encoder of the present one embodiment, thecomparing section makes the light-receiving devices arranged in thelight-on portion corresponding region and the light-receiving devicesarranged in the light-off portion corresponding region correspond toeach other one to one in order of arrangement in the one direction andtakes a difference between the outputs of the light-receiving devicepair that correspond to each other one to one. That is, the differencebetween the outputs of which the phases are shifted by 180° with respectto the movement frequency is taken. As a result, the background noisecan be removed with high accuracy. Therefore, the passing of thelight-on portion and the light-off portion of the moving object can bedetected with high accuracy. Moreover, the light-receiving devices havethe same dimensions in the one direction and are arranged at commonconstant pitches in the light-on portion corresponding region and thelight-off portion corresponding region. Therefore, the group of thedifferential signals obtained from the plurality of light-receivingdevice pairs come to have mutually different phases depending on theorder of arrangement of the plurality of light-receiving device pairs(i.e., the order of arrangement of the light-receiving devices thatconstitute the pairs in the light-on portion corresponding region andthe light-off portion corresponding region) and same pulsewidth.Therefore, by the logical operating section carrying out operation oflogical values expressed by the differential signals, for example, bytaking an exclusive-OR (EXOR), an output signal having a frequencyhigher than the movement frequency and a constant duty ratio can beformed.

In the photoelectric encoder of one embodiment, a waveform shapingsection that shapes a waveform of an input to the logical operatingsection so that rise and fall of the waveform become steep.

When the movement frequency of the moving object is set low, thewaveform changes in the outputs of the light-receiving devices becomegentle, and the rise and fall of the waveforms of the inputs to thelogical operating section also become gentle. Therefore, it is possiblethat a chattering phenomenon (phenomenon that high and low levelsfrequently change in a short time, causing instability) might occur inthe output signal of the logical operating section as a consequence ofchanges in the inputs to the logical operating section across thethreshold value for the logical operation under the influences of noiseand the like during the rise or fall of the inputs to the logicaloperating section. Accordingly, in the photoelectric encoder of thepresent one embodiment, the waveform shaping section shapes thewaveforms of the inputs to the logical operating section so that therise and fall of the waveform become steep. As a result, the inputs tothe logical operating section become hard to receive the influences ofnoise and the like, and the chattering phenomenon can be prevented fromoccurring.

The photoelectric encoder of one embodiment, comprises:

a waveform shaping section that shapes a waveform of the differentialsignal outputted from the comparing section so that rise and fall of thewaveform become steep, wherein

an output of the waveform shaping section is inputted to the logicaloperating section.

In the photoelectric encoder of the present one embodiment, the input tothe logical operating section becomes hard to receive the influences ofnoise and the like, and the chattering phenomenon can be prevented fromoccurring.

In the photoelectric encoder of one embodiment, the comparing sectioncomprises logarithmic amplifiers corresponding to the respectivelight-receiving device pairs, and

each of the logarithmic amplifiers logarithmically amplifies adifference between the outputs of the corresponding light-receivingdevice pairs.

In the photoelectric encoder of the present one embodiment, each of thelogarithmic amplifiers of the comparing section logarithmicallyamplifies the difference between the outputs of the correspondinglight-receiving device pair. Therefore, the SN ratio (signal-to-noiseratio) can be secured even with faint light incident on each of thelight-receiving devices, and this is useful.

In the photoelectric encoder of one embodiment, the comparing sectioncomprises amplifiers corresponding to the light-receiving device pairs,and

the photoelectric encoder comprises:

an identical supply current circuit for supplying a current to each ofthe amplifiers.

In the photoelectric encoder of the present one embodiment, an identicalsupply current circuit supplies a current to each of the amplifiers ofthe comparing section. Therefore, the amplification factor of each ofthe amplifiers can easily be uniformed identical. Therefore, theaccuracy of the output signal is increased.

In the photoelectric encoder of one embodiment, the comparing sectioncomprises amplifiers corresponding to the respective light-receivingdevice pairs,

the plurality of amplifiers are arranged in the one direction along anarray constructed of the plurality of light-receiving devices, and

a center position of the array constructed of the plurality oflight-receiving devices and a center position of an array constructed ofthe plurality of amplifiers coincide with each other in the onedirection.

In the photoelectric encoder of the present one embodiment, the centerposition of the array constructed of the plurality of light-receivingdevices and the center position of the array constructed of theplurality of amplifiers coincide with each other in the one direction.Therefore, the length of each of the wiring lines from the plurality oflight-receiving devices to the plurality of amplifiers can be uniformedcomparatively satisfactorily. Therefore, the variation in the signaldelay and so on attributed to the differences in the length of thewiring lines can be suppressed. As a result, the accuracy of the outputsignal is increased.

In the photoelectric encoder of one embodiment, the comparing sectioncomprises amplifiers corresponding to the respective light-receivingdevice pairs, and

the plurality of amplifiers are arranged in a center portion of asemiconductor chip on which the plurality of light-receiving devices arearranged in common.

In the photoelectric encoder of the present one embodiment, theplurality of amplifiers are arranged in a center portion of asemiconductor chip on which the plurality of light-receiving devices arearranged in common. That is, the plurality of amplifiers are gathered inthe center portion of the semiconductor chip. With the arrangement,variation in the manufacturing processes and variation ascribed to astress and so on are suppressed between the amplifiers.

Moreover, when the plurality of amplifiers are arranged in the centerportion of the semiconductor chip as described above, it is desirable toarrange the logical operating section, the output circuit section foramplifying the output of the logical operating section and the outputterminal for taking out the output of the output circuit section to theoutside of the semiconductor chip at the periphery of the semiconductorchip (i.e., periphery that surrounds the plurality of amplifiers). Thisarrangement results in the adjacent location of the logical operatingsection to the output terminal via the output circuit section, andtherefore, a wiring resistance from the logical operating section to theoutput terminal can be reduced.

In the photoelectric encoder of one embodiment, the comparing sectioncomprises amplifiers corresponding to the respective light-receivingdevice pairs, and

amplifiers, whose logical values expressed by the outputted differentialsignals are subjected to operation by the logical operating section,among the plurality of amplifiers are arranged mutually adjacently.

In the photoelectric encoder of the present one embodiment, theamplifiers, whose logical values expressed by the outputted differentialsignals are subjected to operation by the logical operating sectionamong the plurality of amplifiers, are arranged mutually adjacently.With the arrangement, the wiring lines that lead the outputs of theamplifiers to the logical operating section are simplified. Therefore,mutual influences between the differential signals outputted from theamplifiers and variation in the wiring resistance and so on aresuppressed.

In the photoelectric encoder of one embodiment, the comparing sectionuses the outputs of the light-receiving devices, which are arranged inthe light-off portion corresponding region, of the light-receivingdevice pairs as reference inputs.

In this case, the “reference input” means the input that becomes anegative input of two inputs. For example, assuming that a differencebetween two inputs A and A′ is (A−A′), then the reference input is A′.

In the photoelectric encoder of the present one embodiment, thecomparing section uses the output of the light-receiving device arrangedin the light-off portion corresponding region of each of thelight-receiving device pairs as the reference input (i.e., negativeinput) among the light-receiving device pairs. Therefore, the group ofthe differential signals obtained from the plurality of light-receivingdevice pairs comes to have same pulsewidth and phases different bycertain angles in order of arrangement of the light-receiving devicepairs within a phase shift of 180° with respect to the movementfrequency. Therefore, by the logical operating section carrying outoperation of the logical values expressed by the differential signals,for example, by taking an exclusive-OR (EXOR), an output signal that hasa frequency higher than the movement frequency and a constant duty ratio(meaning a high-level period/cycle in a cyclic signal that repeats ahigh-level period and a low-level period) can be formed with highaccuracy.

In the photoelectric encoder of one embodiment, the logical operatingsection carries out operation by distributing signals, which areobtained from the plurality of light-receiving devices arranged in alight-on portion corresponding region that corresponds to the light-onportion of the moving object, into a plurality of groups in order ofarrangement of the plurality of light-receiving devices and obtains aplurality of output signals that have mutually different phases.

In the photoelectric encoder of the present one embodiment, the logicaloperating section obtains a plurality of output signals that havemutually different phases by carrying out operation with distributingthe signals obtained from the plurality of light-receiving devices intoa plurality of groups on the basis of the order of arrangement of theplurality of light-receiving devices. As a result, the plurality ofoutput signals that have a frequency higher than the movement frequencyand mutually different phases can be obtained.

It is noted that the logical operating section should desirably obtain aplurality of output signals with mutually different phases by carryingout operation with distributing the difference signals obtained from theplurality of light-receiving device pairs into a plurality of groups onthe basis of the order of arrangement of the plurality oflight-receiving device pairs.

In the photoelectric encoder of one embodiment, the logical operatingsection cyclically distributes the signals obtained from the pluralityof light-receiving devices arranged in the light-on portioncorresponding region into a plurality of groups in order of arrangementof the plurality of light-receiving devices in the one direction.

In the photoelectric encoder of the present one embodiment, a pluralityof output signals that have a frequency higher than the movementfrequency and phases mutually different by certain angles are obtained.The obtained plurality of output signals becomes hard to receive theinfluence of the variation in the quantity of light depending on thelight-emitting devices.

In the photoelectric encoder of one embodiment, the logical operatingsection distributes the signals obtained from the plurality oflight-receiving devices arranged in the light-on portion correspondingregion into two groups.

In the photoelectric encoder of the present one embodiment, two outputsignals that have a frequency higher than the movement frequency andphases mutually different by 90° are obtained. The obtained two outputsignals become hard to receive the influences of variation in thequantity of light depending on the light-emitting devices.

The logical operating section should desirably distribute thedifferential signals obtained from the plurality of light-receivingdevice pairs alternately into two groups in order of arrangement in onedirection of the plurality of light-receiving device pairs.

In the photoelectric encoder of one embodiment, the plurality oflight-receiving devices arranged in the light-on portion correspondingregion are arranged at a constant pitch in the one direction, and endsof the light-receiving devices are correspondingly arranged on linesobtained by dividing the light-on portion corresponding region at equalintervals at the pitch.

In the photoelectric encoder of the present one embodiment, theplurality of light-receiving devices arranged in the light-on portioncorresponding region output the signals that have mutually differentphases and same pulsewidth. As a result, the logical operating sectionis able to form output signals that have a frequency higher than themovement frequency and a constant duty ratio. Moreover, since the endsof the light-receiving devices are correspondingly arranged on the lineobtained by dividing the light-on portion corresponding region at equalintervals by the pitch, the dimension of each of the light-receivingdevices can be maximized in each of the regions divided in the onedirection. Therefore, the light-receiving surface of each of thelight-receiving devices can be widened to allow the sensitivity to beimproved.

In the photoelectric encoder of one embodiment, k (k: natural number ofnot smaller than two) light-receiving devices are arranged in thelight-on portion corresponding region that corresponds to the light-onportion of the moving object in the one direction.

In the photoelectric encoder of the present one embodiment, the klight-receiving devices arranged in the light-on portion correspondingregion output k signals that have mutually different phases. Therefore,by the logical operating section carrying out operation of the logicalvalues expressed by the outputs of the light-receiving devices, forexample, by taking an exclusive-OR (EXOR), an output signal of afrequency k times as high as the movement frequency can be formed.

In the photoelectric encoder of one embodiment, k is not smaller thanthree, and the logical operating section takes an exclusive-OR by addingthe logical values expressed by the outputs of the light-receivingdevices in order in which the light-receiving devices adjoin in the onedirection.

Generally, in the case where an exclusive-OR is taken when there arethree or more logical values, operation is first carried out byselecting two logical values, and operation is carried out by addinganother logical value to the operation result, the operations beingrepeated. Since the photoelectric encoder has various variationconditions such as variation in the quantity of light depending on thelight-emitting devices and assembly variation, the accuracy is increasedby regularly carrying out the operation sequence. In this case, thephotoelectric encoder of the present one embodiment takes anexclusive-OR by sequentially adding the logical values expressed by theoutputs of the light-receiving devices in the order in which thelight-receiving devices adjoin in the one direction. Therefore, theobtained output signal becomes hard to receive the influence of thevariation in the quantity of light depending on the light-emittingdevices and so on.

In the photoelectric encoder of one embodiment, k is not smaller thanthree, and the logical operating section takes an exclusive-OR by addingthe logical values expressed by the outputs of the light-receivingdevices in order from the light-receiving devices arranged at oppositeend portions in the one direction in the light-on portion correspondingregion alternately toward the light-receiving devices arranged in acenter portion.

Also, in the photoelectric encoder of the present one embodiment, theobtained output signal similarly becomes hard to receive the influenceof the variation in the quantity of light depending on thelight-emitting device and so on.

In the photoelectric encoder of one embodiment, the logical operatingsection distributes signals obtained from the plurality oflight-receiving devices arranged in a light-on portion correspondingregion that corresponds to the light-on portion of the moving objectinto two groups that have phases mutually different by 90° and takes anexclusive-OR of the signals that have phases mutually different by 90°.

In the photoelectric encoder of the present one embodiment, the logicaloperating section distributes the signals obtained from the plurality oflight-receiving devices arranged in the light-on portion correspondingregion that corresponds to the light-on portion of the moving objectinto two groups that have phases mutually different by 90° and takes anexclusive-OR of the signals that have phases mutually different by 90°.Therefore, if the exclusive-OR is taken only once, an output signal thathas a frequency double the movement frequency is obtained, and this isuseful.

In the photoelectric encoder of one embodiment, a delay section thatdelays an output signal formed by the logical operating section withrespect to a signal inputted to the logical operating section.

When the output signal formed by the logical operating section is takenout of the semiconductor chip, the quantity of current is sometimesincreased to make the output signal have low impedance. In such a case,the voltage change becomes large when the level of the output signalchanges between high and low levels. Therefore, it is concerned thatsuch a voltage change is fed back to the input of the logical operatingsection and causes malfunction. Accordingly, the photoelectric encoderof the present one embodiment has a delay section to delay the outputsignal formed by the logical operating section with respect to thesignal inputted to the logical operating section. With this arrangement,such a malfunction is prevented.

The photoelectric encoder of one embodiment comprises:

an output section that includes a transistor for amplifying the outputsignal formed by the logical operating section, wherein

the transistor has a base current that is a power voltage dependencecurrent.

In the photoelectric encoder of the present one embodiment, the basecurrent of the transistor of the output circuit section is the powervoltage dependence current. For example, if the transistor is an npntransistor, the capability of extracting the current is improved whenthe base current is served as a power voltage dependence type.Therefore, even when electric charge is accumulated by the turbulence ofstatic electricity or the like, the output circuit section and,consequently, the photoelectric encoder are suppressed from malfunction.

The electronic equipment of the present invention is provided with thephotoelectric encoder of the present invention.

In the electronic equipment of the present invention, the photoelectricencoder detects the passing of the light-on portion and the light-offportion of the moving object with high accuracy. Therefore, appropriateoperation can be carried out by using the detection result.

In another aspect, the photoelectric encoder of the present inventioncomprises:

a light-emitting device;

a plurality of light-receiving devices which are arranged in onedirection in a region that light from the light-emitting device canreach; and

a moving object that has a light-on portion and a light-off portion,which alternately pass through a prescribed position corresponding toeach of the light-receiving devices along the one direction and producesa state in which the light is incident on the light-receiving device anda state in which the light is not incident on the light-receivingdevice, respectively, when the portions pass through the position, inwhich

an output of each of the light-receiving devices takes a valuecorresponding to incidence of light or nonincidence of light from thelight-emitting device on the light-receiving device, and furthercomprises:

a logical operating section for forming an output signal that has afrequency different from the movement frequency through operation oflogical values expressed by the outputs of the light-receiving devices.

Furthermore, in an aspect in which the photoelectric encoder is limitedto a light transmission type, the following structure is provided. Thatis, the photoelectric encoder of the light transmission type of thepresent invention comprises:

a light-emitting device;

a plurality of light-receiving devices that face the light-emittingdevice and are arranged in one direction; and

a moving object having a light-transmitting portion and alight-shielding portion that alternately pass between the light-emittingdevice and each of the light-receiving devices at a prescribed movementfrequency along the one direction, in which

an output of each of the light-receiving devices takes a valuecorresponding to an event that light from the light-emitting device istransmitted through the light-transmitting portion or an event that thelight is shielded by the light-shielding portion, the event occurring onthe light-receiving device, and further comprises:

a logical operating section for forming an output signal that has afrequency higher than the movement frequency through operation oflogical values expressed by the outputs of the light-receiving devices.

In the photoelectric encoder of the light transmission type of thepresent invention, the light-transmitting portion and thelight-shielding portion of the moving object alternately pass at theprescribed movement frequency between the light-emitting device and eachof the light-receiving devices along one direction in which thelight-receiving devices are arranged. In accordance with the passing ofthe light-transmitting portion and the light-shielding portion of themoving object sequentially through the position corresponding to theplurality of light-receiving devices, the output values of the pluralityof light-receiving devices sequentially change. Then, the logicaloperating section forms an output signal that has a frequency higherthan the movement frequency by carrying out operation of the logicalvalues expressed by the outputs of the light-receiving devices.Therefore, the resolution can be improved, and the movement informationof the moving speed and the moving direction of the moving object can beobtained more accurately. Moreover, since this is possible even with thepitch of the light-transmitting portions maintained regardless of thepitch of the light-transmitting portions provided at the moving object,the problems of a reduction in the SN ratio and the crosstalk do notoccur.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a view schematically showing the arrangement of a movingobject and a light-receiving device in a photoelectric encoder of oneembodiment of the present invention;

FIG. 2 is a view showing the outputs of the light-receiving devices inFIG. 1 and output signals obtained through operation of logical valuesexpressed by the outputs;

FIG. 3 is a view schematically showing a state in which thelight-receiving devices are arranged in a slit corresponding region anda light-off portion corresponding region;

FIG. 4 is a view schematically showing a state in which fourlight-receiving devices are arranged in each of the slit correspondingregion and the light-off portion corresponding region;

FIG. 5 is a view showing the outputs of the light-receiving devices inFIG. 4;

FIG. 6 is a diagram showing the construction of a comparing section anda logic circuit section provided for the photoelectric encoder of oneembodiment;

FIG. 7 is a view showing a state in which eight light-receiving devicesare arranged in each of the slit corresponding region and the light-offportion corresponding region, and the light-receiving devices aredistributed into two groups alternately in order of arrangement alongthe rotating direction of the moving object;

FIG. 8 is a view schematically showing by comparison the arrangement ofthe light-receiving devices in the prior art example and the arrangementof the light-receiving devices in one embodiment with respect to themoving object;

FIG. 9 is a view showing by comparison the outputs of thelight-receiving devices in the prior art example shown in FIG. 8 and theoutputs of the light-receiving devices in one embodiment;

FIG. 10 is a view showing the construction of a detection section of thephotoelectric encoder of one embodiment;

FIG. 11 is a view schematically showing the arrangement of a movingobject and light-receiving devices in the photoelectric encoder of aprior art example;

FIG. 12A is a diagram schematically showing the spatial arrangement of amoving object, a light-emitting section and a light-receiving section ina photoelectric encoder of the light transmission type;

FIG. 12B is a diagram schematically showing the spatial arrangement of amoving object, a light-emitting section and a light-receiving section ina photoelectric encoder of the light reflection type;

FIG. 13 is a view schematically showing the waveforms of signalsobtained from the outputs of the eight light-receiving devices of FIG.7;

FIG. 14 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 15 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 16 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 17 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 18 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 19 is a view for schematically explaining the logical operationcarried out by using the signals in FIG. 13;

FIG. 20 is a diagram schematically showing the equivalent circuit of oneIIL device;

FIG. 21 is a block diagram showing the circuit construction of a logiccircuit section constructed of IIL devices to execute the logicaloperation shown in FIG. 18;

FIG. 22 is a block diagram showing the construction of the photoelectricencoder of a prior art example;

FIG. 23 is a block diagram showing the construction of the photoelectricencoder of one embodiment of the present invention adapted to executethe logical operation shown in FIG. 18;

FIG. 24 is a block diagram showing the circuit construction of thedifferential amplifier in FIG. 23;

FIG. 25 is a diagram showing an example in which the current supplysource of each of the differential amplifiers is constructed of anidentical supply current circuit;

FIG. 26 is a view schematically showing the layout of thelight-receiving devices and the differential amplifiers on asemiconductor substrate in the photoelectric encoder of the oneembodiment;

FIG. 27 is a view schematically showing the arrangement of the slits andthe light-off portion of the moving object and the light-receivingdevices in the photoelectric encoder of the one embodiment;

FIG. 28 is a view showing the concrete arrangement of the photoelectriccurrent output port of the light-receiving device;

FIG. 29 is a view illustrating the block construction in which awaveform shaping section is provided immediately before the logiccircuit section;

FIG. 30A is a diagram showing a circuit example that constitutes thewaveform shaping section;

FIG. 30B is a diagram showing another circuit example that constitutesthe waveform shaping section;

FIG. 31A is a graph showing the signal waveforms of portions when thewaveform shaping section is not provided;

FIG. 31B is a graph showing the signal waveforms of the portions whenthe waveform shaping section is provided;

FIG. 32 is a view showing an example in which the semiconductorsubstrate is mounted on the header portion of a lead frame;

FIG. 33 is a view showing an example in which the same semiconductorsubstrate as the one shown in FIG. 32 is mounted on the header portionof another lead frame; and

FIG. 34 is a diagram showing a structural example in which the basecurrent of the transistor of the amplifier circuit that constitutes anoutput circuit section is of the power voltage dependence type.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail below by theembodiments shown in the drawings.

FIG. 10 shows the cross section of the detection section of thephotoelectric encoder of the light transmission type of one embodiment.In the photoelectric encoder, a light-emitting section 142 is lodged onone side (upper side in FIG. 10) of a casing 145 that has a slot 147 atan approximate center, and a light-receiving section 144 is lodged onthe other side (lower side in FIG. 10). With this arrangement, thelight-emitting section 142 and the light-receiving section 144 face eachother. The light-emitting section 142 is constituted by mounting asemiconductor light-emitting chip 141 that serves as a light-emittingdevice on a header portion 148 a of a lead frame 148 and sealing thesame with a transparent resin 152. The light-receiving section 144 isconstituted by mounting a semiconductor light-receiving chip 10 thatincludes a plurality of light-receiving devices on the header portion149 a of a lead frame 149 and sealing the same with a transparent resin154. A collimating lens 146 for making parallel the light emitted fromthe light-emitting section 142 is arranged in front of thelight-emitting section 142 on an optical axis 150 that connects thesemiconductor light-emitting chip 141 with the semiconductorlight-receiving chip 10. A disk-shaped moving object 40 that has aplurality of slits (collectively denoted by the reference letter X) asthe light-on portion is inserted in the slot 147.

In operation, the moving object 40 is rotated at a constant speed aroundthe central axis (not shown) parallel to the optical axis 150. Thelight-emitting chip 141 is electrified through the lead frame 148 tomake the light-emitting chip 141 emit light, and the light is emittedalong the optical axis 150 via the collimating lens 146. Thelight-receiving chip 10 photoelectrically converts the light incidentthrough the slit X of the moving object 40 and outputs a signalcorresponding to the quantity of incident light. The output of thelight-receiving chip 10 is processed by a comparing section and alogical operating section as described later.

It is noted that the light-receiving chip 10 is divided into a pluralityof light-receiving devices in the following examples (the devices may bea plurality of photodetection regions in a single chip).

At the top of FIG. 1, the portions where slits X1, X2, . . . of themoving object 40 are provided are schematically shown, which are viewedperpendicularly to the plate surface. The portions where the platematerial exists between the slits X1, X2, . . . constitute light-offportions Y1, Y2, . . . where no light is made incident on thelight-receiving chip 10. At the bottom of FIG. 1, the light-receivingchip 10 (divided light-receiving devices are indicated by referencenumerals 11 a, 11 b, . . . ) is schematically shown. In FIG. 1, therotating direction D of the moving object 40 is indicated as a straightline in approximation (the same thing can be said for the followingfigures). The moving object 40 has the slits X1, X2, . . . and thelight-off portions Y1, Y2, . . . alternately at a constant pitch P alongthe rotating direction D. The slits X1, X2, . . . and the light-offportions Y1, Y2, . . . have the same dimension of 1/2 pitch (i.e., P/2)in the rotating direction D. With this arrangement, same number oflight-receiving devices can be arranged in a region 20 corresponding tothe slit X1 (referred to as a “slit corresponding region”) and a region21 corresponding to the light-off portion Y1 (referred to as a“light-off portion corresponding region”) in the rotating direction D.

In the example of FIG. 1, a plurality of the light-receiving devices 11a, 11 b, . . . , are arranged at a constant pitch along the rotatingdirection D in the slit corresponding region 20. The light-receivingdevices 11 a, 11 b, . . . , have same dimension along the rotatingdirection D.

When the moving object 40 is rotated at a constant speed as describedabove in operation, the slits X1, X2, . . . and the light-off portionsY1, Y2, . . . alternately pass at a constant movement frequency (assumedto be f) along the rotating direction D with respect to thelight-receiving devices 11 a, 11 b, . . . In counting the movementfrequency f, the individual slits X1, X2, . . . are not distinguished,and it is assumed that the passing of any one of the slits X1, X2, . . .is counted one time.

At this time, as shown in FIG. 2, outputs A1+, A2+, . . . of thelight-receiving devices 11 a, 11 b, . . . take a high-level valuecorresponding to the transmission of light from the light-emitting chip41 through the slits X1, X2, . . . of the moving object 40 or alow-level value corresponding to the interruption of light by thelight-off portions Y1, Y2, . . . with respect to the light-receivingdevices. Then, the outputs A1+, A2+, . . . change at a constantfrequency equal to the movement frequency f and with mutually differentphases. The present invention intends to obtain an output signal thathas a frequency higher than the movement frequency f by carrying outoperation of the logical values (high level is assumed to be logic 1,and low-level is assumed to be logic 0) expressed by the plurality ofoutputs A1+, A2+, . . . For example, as shown in FIG. 13, it is assumedthat eight signals A1, B1, A2, B2, . . . A4, B4 that have the samefrequency (movement frequency f) and sequentially different phasesdepending on the light-receiving devices are obtained. As shown in FIG.14, the signals are combined by twos in the combinations of (A1, A3)(B1, B3) (A2, A4) (B2, B4) in this example, and the respectiveexclusive-OR's (EXOR's) are taken. As a result, four signals A11, B11,A12 and B12, which have a double frequency 2 f and phases mutuallydifferent by 45°, can be obtained. As described above, by taking anexclusive-OR (EXOR), an output signal of a frequency higher than themovement frequency f can easily be formed. It is noted that the dutyratio of each signal in FIGS. 13 and 14 is 1/2 (i.e., high-level periodlow-level period=1:1).

FIG. 3 shows an example in which same number of light-receiving devicesare arranged in the slit corresponding region 20 and the light-offportion corresponding region 21 in the rotating direction D. With thisarrangement, by taking a difference between the outputs A1+, A2+, . . .of the light-receiving devices 11 a, 11 b, . . . arranged in the slitcorresponding region 20 and the outputs A1−, A2−, . . . of thelight-receiving devices 12 a, 12 b, . . . arranged in the light-offportion corresponding region 21, the background noise can be removed.Therefore, the passing of the slits X1, X2, . . . and the light-offportions Y1, Y2, . . . of the moving object 40 can be detected with highaccuracy.

FIG. 4 shows an example in which the regularity (constant pitch and samedimension) of the arrangement of the light-receiving devices describedwith reference to FIGS. 1 and 3 is provided, and more concretelyarranged are four light-receiving devices 11 a, 11 b, 11 c and 11 d inthe slit corresponding region 20 and four light-receiving devices 12 a,12 b, 12 c and 12 d in the light-off portion corresponding region 21.The light-receiving devices 11 a, 11 b, 11 c and 11 d output the signalsA1+, A2+, A3+ and A4+, and the light-receiving devices 12 a, 12 b, 12 cand 12 d output the signals A1−, A2−, A3− and A4−. As shown in FIG. 5,the outputs A1+, A2+, A3+ and A4+ of the plurality of light-receivingdevices 11 a, 11 b, 11 c and 11 d arranged in the slit correspondingregion 20 sequentially change at a constant movement frequency f andwith phases mutually different by prescribed angles. Likewise, theoutputs A1−, A2−, A3− and A4− of the light-receiving devices 12 a, 12 b,12 c and 12 d arranged in the light-off portion corresponding region 21sequentially change at the constant movement frequency f and with phasesmutually different by prescribed angles. The outputs A1+, A2+, A3+ andA4+ and the outputs A1−, A2−, A3− and A4− have phases mutually differentby 180°. That is, the phases are inverted.

FIG. 6 shows a comparing section 45 that processes the outputs of thelight-receiving devices and a logic circuit section 46 as a logicaloperating section that receives the outputs of the comparing section 45through a digital conversion circuit (not shown).

The comparing section 45 includes four comparators 41, 42, 43 and 44.The comparator 41 takes a difference between the outputs A1+, A1− of thelight-receiving devices 11 a and 12 a, the comparator 42 takes adifference between the outputs A2+, A2− of the light-receiving devices11 b and 12 b, the comparator 43 takes a difference between the outputsA3+, A3− of the light-receiving devices 11 c and 12 c, and thecomparator 44 takes a difference between the outputs A4+, A4− of thelight-receiving devices 11 d and 12 d. That is, in this example, thelight-receiving devices 11 a, 11 b, 11 c and 11 d arranged in the slitcorresponding region 20 and the light-receiving devices 12 a, 12 b, 12 cand 12 d arranged in the light-off portion corresponding region 21 aremade to correspond to each other one to one in order of arrangement inthe rotating direction D. Moreover, the outputs A1−, A2−, A3− and A4−that have a negative sign serve as reference inputs. That is, theoutputs A1−, A2−, A3− and A4− are subtracted from the outputs A1+, A2+,A3+ and A4+, respectively. By thus taking differences by the comparators41, 42, 43 and 44, the background noise can be removed. Therefore, thepassing of the slits X1, X2, . . . and the light-off portions Y1, Y2, .. . of the moving object 40 can be detected with high accuracy.

The logic circuit section 46 is constructed of an exclusive-OR circuitthat takes an exclusive-OR (EXOR) of the logical values expressed by theoutputs of the comparators 41, 42, 43 and 44. The output of theexclusive-OR changes from logic 1, logic 0, logic 1, . . . as the numberof inputs of logic 1 changes from an odd number, an even number, an oddnumber, . . . Therefore, an output signal A of a frequency higher thanthe movement frequency f can easily be formed. In this four-inputexample, an output signal A having a frequency 4 f that is four times ashigh as the movement frequency f can be formed. Moreover, based on theregularity (constant pitch and same dimension) of the arrangement of thelight-receiving devices, the output signal A comes to have a constantduty ratio.

FIG. 7 shows an example in which the regularity (constant pitch and samedimension) of the arrangement of the light-receiving devices describedwith reference to FIGS. 1 and 3 is provided, and more concretelyarranged are eight light-receiving devices 11 a, 11 b, 11 c, 11 d, 11 e,11 f, 11 g and 11 h in the slit corresponding region 20 and eightlight-receiving devices 12 a, 12 b, 12 c, 12 d, 12 e, 12 f, 12 g and 12h in the light-off portion corresponding region 21. The light-receivingdevices 11 a, 11 b, 11 c, 11 d, 11 e, 11 f, 11 g and 11 h output signalsA1+, B1−, A2+, B2−, A3+, B3−, A4+ and B4−, respectively, and thelight-receiving devices 12 a, 12 b, 12 c, 12 d, 12 e, 12 f, 12 g and 12h output signals A1−, B1+, A2−, B2+, A3−, B3+, A4− and B4+.

In this example, the comparing section 45 shown in FIG. 6 takes adifference between the outputs A1+ and A1− of the light-receiving devicepair 11 a and 12 a, a difference between the outputs A2+ and A2− of thelight-receiving device pair 11 c and 12 c, a difference between theoutputs A3+ and A3− of the light-receiving device pair 11 e and 12 e,and a difference between the outputs A4+ and A4− of the light-receivingdevice pair 11 g and 12 g. Then, the logic circuit section 46 shown inFIG. 6 takes an exclusive-OR (EXOR) of the logical values expressed bythe outputs of the four comparators 41, 42, 43 and 44. As a result, anoutput signal A having a frequency 4 f that is four times as high as themovement frequency f is formed.

Moreover, by a comparing section having the same construction as that ofthe comparing section 45 shown in FIG. 6 takes a difference between theoutputs B1+ and B1− of the light-receiving device pair 12 b and 11 b, adifference between the outputs B2+ and B2− of the light-receiving devicepair 12 d and 11 d, a difference between the outputs B3+ and B3− of thelight-receiving device pair 12 f and 11 f, and a difference between theoutputs B4+ and B4− of the light-receiving device pair 12 h and 11 h.Then, a logic circuit section of the same construction as that of thelogic circuit section 46 shown in FIG. 6 takes an exclusive-OR (EXOR) ofthe logical values expressed by the outputs of the comparing section(four comparators). As a result, an output signal B having a frequency 4f that is four times as high as the movement frequency f is formed.

The arrangement of the light-receiving devices (photodiode) of the priorart example shown in the middle of FIG. 1 is shown in the middle of FIG.8, and the arrangement of the light-receiving devices shown in FIG. 7 isshown at the bottom of FIG. 8 by comparison to it. In the prior artexample, as shown in FIG. 9, each of output signals A0 and B0 had thesame frequency f as the movement frequency f and phases mutuallydifferent by 90°. In contrast to this, when the output of thelight-receiving device is subjected to the processing in the arrangement(arrangement shown in FIG. 7) of the light-receiving devices shown atthe bottom of FIG. 8, the output signals A and B come to have afrequency 4 f that is four times as high as the movement frequency f andphases mutually different by 90°.

With this arrangement, the resolution can be improved, and the movementinformation of the moving speed, the moving direction and so on of themoving object 40 can be obtained more accurately. Moreover, since thisis possible even with the pitch of the slits X1, X2, . . . maintainedregardless of the pitch of the slits X1, X2, . . . provided at themoving object 40, the problems of the reduction in the SN ratio and thecrosstalk do not occur.

In general, in the case where an exclusive-OR is taken when there arethree or more logical values, operation is first carried out byselecting two logical values, and operation is carried out by addinganother logical value to the operation result, the operations beingrepeated. Since the photoelectric encoder has various variationconditions such as variation in the quantity of light depending on thelight-emitting chip 41 and assembly variation, the accuracy is increasedby regularly carrying out the operation sequence.

In this case, the logic circuit section 46 should desirably take anexclusive-OR by successively adding the logical values expressed by thelight-receiving devices 11 a, 11 b, . . . in order in which thelight-receiving devices 11 a, 11 b, . . . adjoin in the rotatingdirection D. As a result, the obtained output signal becomes hard toreceive the influence of the variation in the quantity of lightdepending on the light-emitting chip 41 and the like.

Moreover, the logic circuit section 46 may take an exclusive-OR byadding the logical values expressed by the light-receiving devices 11 a,11 b, . . . in order from the light-receiving devices 11 a, 11 b, . . .arranged at opposite end portions inside the slit corresponding region20 toward the light-receiving devices 11 a, 11 b, . . . arranged in thecenter portion alternately in the rotating direction D. Also, in thiscase, the obtained output signal becomes hard to receive the influenceof the variation in the quantity of light depending on thelight-emitting chip 41 and the like.

Explanation is next made to a case where the logical operation iscarried out a plurality of times.

For example, first, as shown in the left half of FIG. 15, anexclusive-OR (EXOR) is taken by combining eight signals A1, B1, A2, B2,. . . , A4, B4 that have same frequency (movement frequency f) andsequentially different phases obtained by the light-receiving devices bytwos in, for example, the combinations of (A1, A3) (B1, B3) (A2, A4)(B2, B4) in this example. As a result, similar to the description withreference to FIG. 14, four signals A11, B11, A12 and B12, which have adouble frequency and phases sequentially different by 45° are obtained.Subsequently, as shown in the right half of FIG. 15, an exclusive-OR(EXOR) is taken by combining the signals by twos in, for example, thecombinations of (A11, A12) (B11, B12) in this example. As a result, thetwo signals A21 and B21, which have a frequency 4 f that is four timesthe original movement frequency f and a phase mutually different by 90°are obtained. As described above, by taking the exclusive-OR two times,the frequency of the output signal can be increased, and the number ofsignals can be reduced. Further, as shown in FIG. 16, a signal A31having a frequency 8 f that is eight times the original movementfrequency f can be formed by taking an exclusive-OR (EXOR) of thesignals A21 and B21. It is noted that the duty ratios of the signals inFIGS. 15 and 16 are each 1/2 (i.e., high-level period:low-levelperiod=1:1).

As described above, by taking an exclusive-OR (EXOR) of the signals thathave phases mutually different by 90° a plurality of times, a signalthat has a frequency double the original movement frequency can beobtained. Then, by repetitively carrying out the operation a pluralityof times, a signal having a frequency that is integral multiple timesthe original movement frequency, or more in detail, 2^(m) times (notethat m is a natural number) as high as the original movement frequencycan be obtained.

Moreover, as shown in, for example, FIG. 17, it is acceptable to obtainfour signals A11, B11, A12 and B12 that have a double frequency andphases sequentially different by 45° and thereafter take an exclusive-OR(EXOR) of the combinations of (A11, B11) (A12, B12) unlike the foregoingexample. As a result, two signals A22 and B22 having a frequency 2 fthat is double the original movement frequency f and phases mutuallydifferent by 90° are obtained. It is noted that the duty ratios of thesignals A22 and B22 are each 3/4 (i.e., high-level period:low-levelperiod=3:1). Further, if the logical product (AND) or nonconjunction(NAND) of the signals A22 and B22 is taken, a signal A31 having afrequency 8 f that is eight times the original movement frequency f canbe formed.

Moreover, as shown in, for example, FIG. 18, it is acceptable to take anexclusive-OR (EXOR) by combining eight signals A1, B1, A2, B2, . . . ,A4, B4 that have same frequency (movement frequency f) and phasessequentially different obtained by the light-receiving devices by twosin, for example, the combinations of (A1, A2) (A3, A4) (B1, B2) (B3, B4)in this example. As a result, four signals A13, A14, B13 and B14, whichhave the same frequency as the movement frequency f and different phasesare obtained. That is, only the phase is different by 90° between thesignals (A13, A14) and between the signals (B13, B14), and the phase isdifferent by 67.5° between the signals (A13, B13). It is noted that theduty ratios of the signals A13, A14, B13 and B14 are each 3/4 (i.e.,high-level period:low-level period=3:1). Next, the logical product (AND)or nonconjunction (NAND) is taken by combining the signals by twos, orin the combinations of (A13, A14) (B13, B14) in this example. As aresult, two signals A21 and B21 having a frequency 4 f that is fourtimes the original movement frequency f and phases mutually different by90° are obtained. Further, as shown in the right half of FIG. 19, it ispossible to form a signal A31 having a frequency 8 f that is eight timesthe original movement frequency f by taking an exclusive-OR (EXOR) ofthe signals A21 and B21.

As described above, by using the logical product (AND) or nonconjunction(NAND) in a certain stage of the logical operation, the logicaloperation becomes simpler than when the exclusive-OR is repetitivelytaken a plurality of times. Therefore, the number of devices thatconstitute the logical operating section can be reduced. As a result,signal processing becomes easy in an IC (Integrated Circuit) provided ina stage subsequent to the photoelectric encoder, and this is useful.

The photoelectric encoder should desirably employ an integratedinjection logic device (hereinafter referred to as IIL device) that hasan equivalent circuit as shown in, for example, FIG. 20 as a constituentelement of the logical operating section. With the arrangement, thelogical operating section can easily be constituted of a bipolar IC.Therefore, it becomes easy to integrally manufacture the light-receivingdevice and the logical operating section. Moreover, since one deviceconstitutes the NAND (nonconjunction) circuit in the IIL device, theconstruction of the logical operating section is simplified when the IILdevice is employed.

For example, when the IIL device is employed as a constituent element ofthe logical operating section, the logical operation shown in FIG. 18 isprovided by a circuit (logical operating section) as shown in FIG. 21.The logical operating section shown in FIG. 21 has an amplifier section(AMP) 50 that amplifies the signals A1, B1, A2, B2, . . . , A4, B4obtained by the light-receiving devices, an exclusive-OR section (EXOR)60 that takes an exclusive-OR and nonconjunction circuits (NAND) 70 and71 that take nonconjunction. The amplifier section (AMP) 50 hasamplifiers 51, 52, . . . , 58 for each signal, and the exclusive-ORsection (EXOR) 60 has exclusive-OR circuits 61, 62, 63 and 64 for eachof two signals (A1, A2) (A3, A4) (B1, B2) (B3, B4). Each of theexclusive-OR circuits 61, 62, 63 and 64 includes two nonconjunctioncircuits (NAND). Since each of the NAND circuits in FIG. 21 isconstructed of one IIL device, the construction of the logical operatingsection is simplified.

FIG. 23 illustrates a schematic block construction of a photoelectricencoder when the logical operation shown in FIG. 14 is carried out.

The photoelectric encoder has a light-receiving section 81, a currentamplification section 82, a diode section 83, a differentialamplification section 84 as the comparing section, an AD conversionsection 85, a logic circuit section 86 as a logical operating section,an output circuit section 87, a constant current circuit 88 and aconstant voltage circuit 89, which are integrally formed on an identicalsemiconductor substrate 80 as the semiconductor chip. Thelight-receiving section 81 includes eight pairs of light-receivingdevices PDA1+ through PDB4− (arranged along the rotating direction D inthe same order as the light-receiving devices 11 a, 11 b, . . . 12 h inFIG. 7 in the real space). The current amplification section 82 includescurrent amplifiers corresponding to the light-receiving devices, and thecurrent amplifiers amplify the outputs of the correspondinglight-receiving devices in the analog state. The diode section 83includes diodes corresponding to the current amplifiers, and the diodesconvert the outputs of the corresponding current amplifiers intovoltages. The differential amplification section 84 includesdifferential amplifiers 51, 52, . . . , 58 corresponding to therespective diode pairs (therefore light-receiving device pairs), and thedifferential amplifiers 51, 52, . . . , 58 amplify differences betweenthe outputs of the corresponding diode pairs through logarithmiccompression. That is, logarithmic amplifiers are constructed of therespective diode pairs and differential amplifiers. Therefore, even whenthe light incident on each of the light-receiving devices is faint, asatisfactory SN ratio (signal-to-noise ratio) can be secured. The ADconversion section 85 includes AD converters ADC1, ADC2, . . . , ADC8corresponding to the differential amplifiers 51, 52, . . . , 58, and theAD converters ADC1, ADC2, . . . , ADC8 subject the outputs of thecorresponding differential amplifiers 51, 52, . . . , 58 toanalog-to-digital conversion and output digital logic values. The logiccircuit section 86 includes exclusive-OR circuits EXOR1, EXOR2, EXOR3and EXOR4 corresponding to the pairs (51, 53) (52, 54) (55, 57) (56, 58)of the differential amplifiers, i.e., the pairs (ADC1, ADC3) (ADC2,ADC4) (ADC5, ADC7) (ADC6, ADC8) of the AD converters. Then, theexclusive-OR circuits EXOR1, EXOR2, EXOR3 and EXOR4 take an exclusive-ORof the outputs of the pairs (51, 53) (52, 54) (55, 57) (56, 58) of thecorresponding differential amplifiers, i.e., between the pairs (ADC1,ADC3) (ADC2, ADC4) (ADC5, ADC7) (ADC6, ADC8) of the AD converters. Theoutput circuit section 87 includes amplifier circuits OC1, OC2, OC3 andOC4 constructed of two transistors corresponding to the exclusive-ORcircuits EXOR1, EXOR2, EXOR3 and EXOR4, and the amplifier circuits OC1,OC2, OC3 and OC4 amplify the outputs of the corresponding exclusive-ORcircuits (EXOR) and output the amplified signals to output terminalsVOA1, VOA2, VOB1 and VOB2. It is noted that VCC represents a terminal towhich the power voltage is supplied, and GND represents a terminalgrounded. The constant current circuit 88 and the constant voltagecircuit 89 supply a constant current and a constant voltage,respectively, to each section of the photoelectric encoder.

FIG. 22 illustrates the schematic construction of a conventionalphotoelectric encoder. The photoelectric encoder has a light-receivingsection 181, a current amplification section 182, a diode section 183, adifferential amplification section 184 as a comparing section, an ADconversion section 185, an output circuit section 187 and a constantvoltage circuit 189, which are integrally formed on an identicalsemiconductor substrate 180. The constituent elements corresponding tothe constituent elements in FIG. 23 are denoted by reference numeralsincreased with increments of one hundred (no description is provided forindividual ones). As is apparent from a comparison between FIG. 22 andFIG. 23, the number of signals handled is increased in the photoelectricencoder shown in FIG. 23. Therefore, the circuit needs matching. Forexample, it is assumed that the differential amplifiers 51, 52, . . . ,58 shown in FIG. 23 are constructed of the circuit 91 shown in FIG. 24.In the differential amplifiers 51, 52, . . . , 58, a current is suppliedfrom a current supply source 90 (included in the constant currentcircuit 88 in FIG. 23). In the case, it is desirable to constitute thecurrent supply source 90 of the differential amplifiers 51, 52, . . . ,58 of an identical supply current circuit as shown in FIG. 25 and supplya current from the supply current circuit to the differential amplifiers51, 52, . . . , 58 (indicated by AMP1, AMP2, AMP3, . . . in FIG. 25).With this arrangement, a current matching can be provided among thedifferential amplifiers 51, 52, . . . , 58, and the amplificationfactors of the differential amplifiers 51, 52, . . . , 58 can easily beuniformed identical. As a result, the accuracy of the output signal canbe improved.

Moreover, since the light-receiving devices PDA1+ through PDB4− have aminute output current of several hundreds of nanoampares, a layout fromthe light-receiving devices PDA1+ through PDB4− to the differentialamplifiers 51, 52, . . . , 58 on the semiconductor substrate 80 isimportant. For example, as shown in FIG. 26, it is desirable that arrays99 a and 99 b constructed of the differential amplifiers 51, 52, . . . ,58 are arranged along an array 98 constructed of the light-receivingdevices PDA1+ through PDB4− (i.e., light-receiving devices 11 a, 11 b, .. . , 12 h), and a center position 98 c of the array 98 constructed ofthe light-receiving devices and the center position 99 c of the arrays99 a and 99 b constructed of the differential amplifiers coincide witheach other in the real space. That is, the array 98 constructed of thelight-receiving devices and the arrays 99 a and 99 b constructed of thedifferential amplifiers should desirably be arranged symmetrically withrespect to a straight line that connects the center positions 98 c with99 c (straight line perpendicular to the direction D on thesemiconductor substrate 80). According to the layout, the length ofwiring lines 97 extending from the plurality of light-receiving devices11 a, 11 b, . . . , 12 h to the plurality of differential amplifiers 51,52, . . . , 58 can be uniformed comparatively satisfactorily. Therefore,variation of signal delay attributed to a difference in the lengthbetween the wiring lines 97 and so on can be suppressed. As a result,the accuracy of the output signal can be improved. Moreover, in thelayout of FIG. 26, the pairs (51, 53) (52, 54) (55, 57) (56, 58) of thedifferential amplifiers whose exclusive-OR is taken are adjacentlyarranged in the direction D. Therefore, the variation of the signaldelay attributed to the difference in the length between the wiringlines from the pairs (51, 53) (52, 54) (55, 57) (56, 58) of thedifferential amplifiers to the exclusive-OR circuits EXOR1, EXOR2, EXOR3and EXOR4 and so on can be suppressed. Therefore, the accuracy of theoutput signal can further be improved.

FIG. 27 shows more in detail the arrangement of the light-receivingdevices 11 a, 11 b, . . . , 12 h (the same arrangement as that of FIG.7). As shown in FIG. 27, the ends of the light-receiving devices 11 a,11 b, . . . , 12 h are arranged in correspondence with lines V, V, . . .obtained by dividing the slit corresponding region 20 and the light-offportion corresponding region 21 at equal intervals in the direction D.Therefore, the dimension of the light-receiving devices 11 a, 11 b, . .. , 12 h can be maximized in the regions divided in the direction D.Therefore, the photodetection surfaces of the light-receiving devices 11a, 11 b, . . . , 12 h can be widened to allow high sensitivity to beachieved.

FIG. 28 shows the concrete arrangement of photoelectric current outputports T1, T2, T3, T4, . . . of the outputs of the light-receivingdevices 11 a, 11 b, 12 h (the ports referred to as “photoelectriccurrent output ports”) (portions concerning the four light-receivingdevices 11 a, 11 b, 11 c and 11 d located at the left end portion areonly shown for the sake of simplicity).

In order to obtain a frequency higher than the movement frequency, it isdesirable to reduce the dimension of the light-receiving devices 11 a,11 b, . . . , 12 h in the direction D for the achievement of highresolution. However, if the dimension of the light-receiving devices ismerely reduced, the area necessary for the photoelectric current outputports of the light-receiving devices cannot be secured, and thearrangement becomes difficult. Accordingly, in this example as shown inFIG. 28, the photoelectric current output ports T1, T2, T3, T4, . . . ofthe light-receiving devices mutually adjacent in the direction D arearranged on the mutually opposite sides of the array 98 constructed ofthe plurality of light-receiving devices 11 a, 11 b, . . . , 12 h in thedirection perpendicular to the direction D. In detail, the photoelectriccurrent output ports T1, T3, . . . of the odd-number light-receivingdevices 11 a, 11 c, . . . from the left end are provided on the upperside (in FIG. 28) of the array 98, while the photoelectric currentoutput ports T2, T4, . . . of the even-number light-receiving devices 11b, 11 d, . . . from the left end are provided on the lower side (in FIG.28) of the array 98. With this arrangement, even when the dimension ofthe light-receiving devices 11 a, 11 b, . . . , 12 h is reduced in thedirection D as shown in FIG. 28, an area necessary for the photoelectriccurrent output ports T1, T2, T3, T4, . . . of the light-receivingdevices can be secured, and the arrangement becomes possible.

FIG. 29 illustrates a block construction in which a waveform shapingsection 79 is provided in place of the AD conversion section 85immediately before the logic circuit section 86 in FIG. 23. It is notedthat a waveform generating section 78 in FIG. 29 is shown inclusive ofthe light-receiving section 81, the current amplification section 82,the diode section 83 and the differential amplification section 84 asthe comparing section shown in FIG. 23.

When the movement frequency f of the moving object 40 is set low, thewaveform changes in the outputs of the light-receiving devices PDA1+through PDB4− (i.e., the light-receiving devices 11 a, 11 b, . . . , 12h) become gentle, and the rise and fall of the waveforms of inputs F3and F4 to the logic circuit section 86 also become gentle as shown inFIG. 31A. Therefore, it is possible that a chattering phenomenon(phenomenon that high and low levels frequently change in a short time)J might occur in the output signal F2 of the logic circuit section 86 asa consequence of changes in the inputs F3 and F4 to the logic circuitsection 86 across the threshold value for the logical operation underthe influences of noise and the like during the rise or fall of theinputs to the logic circuit section 86. In the case, the output F1 ofthe output circuit section 87 also change. Accordingly, in the exampleof FIG. 29, the waveform shaping section 79 shapes the waveforms of theinputs C3 and C4 (C4 in the example) to the logic circuit section 86 sothat the rise and fall of the waveforms become steep as shows in FIG.31B. As a result, the rise and fall of the output waveform C2 of thedifferential amplification section 84 become steep (note that FIG. 31Bis expanded in the horizontal direction (direction of the time base) incomparison with FIG. 31A). As a result, the inputs to the logic circuitsection 86 become hard to receive the influence of noise and the like,and the chattering phenomenon can be prevented from occurring. In thecase, the transition of the output C2 in the logic circuit section 86 isstabilized, and the transition of the output C1 of the output circuitsection 87 is also stabilized.

In concrete, as in the circuit example 79A (part enclosed by the dashedline) shown in FIG. 30A, the waveform shaping section 79 is constructedof a constant-current source 791 and an npn transistor 792 insertedbetween the power source Vcc and the ground GND. The npn transistor 792receives the output of the differential amplification section 84(collector potential of the npn transistor 844) at its base, amplifiesthe output and forms an output at its collector.

It is acceptable to connect the emitter of the npn transistor 792between the emitter of an npn transistor 844 and a resistor 855 locatedon the GND side in the differential amplification section 84 as in thecircuit example 79B shown in FIG. 30B. With the arrangement, the emitterpotential of the npn transistor 792 can be pulled up when the npntransistor 792 is turned on, and this therefore prevents the occurrenceof malfunction.

FIG. 32 shows a mounting example in which the semiconductor substrate 80as the semiconductor chip is mounted on the header portion 149 a of thelead frame 149 in the real space. The lead frame 149 includes a lead pin149 b for grounding continued integrally with the header portion 149 a,a lead pin 149 c to which the power voltage is supplied and four leadpins 149 d, 149 e, 149 f and 149 g for signal output.

In the example, the array 98 constructed of the light-receiving devices11 a, 11 b, . . . , 12 h is arranged along one side (lower side in FIG.32) 80 a on the surface of the semiconductor substrate 80. Moreover, apower terminal VCC and a grounding terminal GND are arranged along aleft side 80 b. Output terminals VOA1 and VOA2 are arranged along anupper side 80 c, and output terminals VOB1 and VOB2 are arranged along aright side 80 d. The lead pins 149 b, 149 c, 149 d, 149 e, 149 f and 149g are connected to the corresponding terminals (bonding pads) GND, VCC,VOA1, VOA2, VOB1 and VOB2 via Au wires 189 b, 189 c, 189 d, 189 e, 189 fand 189 g, respectively.

Moreover, in this example, the differential amplifiers 51, 52, . . . ,58 that constitute the differential amplification section 84 arearranged gathered in the center portion on the surface of thesemiconductor substrate 80, slightly differently from the layout shownin FIG. 26. With the arrangement, variation in the manufacturingprocesses and variation ascribed to a stress and so on can be suppressedbetween the amplifiers.

On the other hand, in this example, as in the layout shown in FIG. 26,the pairs (51, 53) (52, 54) (55, 57) (56, 58) of the differentialamplifiers where an exclusive-OR of the logical values expressed by theoutputted differential signals is taken among the differentialamplifiers 51, 52, . . . , 58 are arranged mutually adjacently.Therefore, although not shown in FIG. 32, by arranging the constituentelements of the logic circuit section 86 and the output circuit section87 shown in FIG. 23 so that the sections surround the differentialamplification section 84, the wiring lines from the pairs (51, 53) (52,54) (55, 57) (56, 58) of the differential amplifiers to the exclusive-ORcircuits EXOR1, EXOR2, EXOR3 and EXOR4 are simplified, and mutualinfluences between the differential signals, variation in the wiringresistance and so on are suppressed. In addition, the variation in thesignal delay and so on attributed to the difference in the lengthbetween the wiring lines can be suppressed. Therefore, the accuracy ofthe output signal can further be improved. Moreover, by virtue of theadjacent location of the logic circuit section 86 to the outputterminals VOA1, VOA2, VOB1 and VOB2 via the output circuit section 87,the wiring resistance from the logic circuit section 86 to the outputterminals VOA1, VOA2, VOB1 and VOB2 can be reduced.

FIG. 33 shows a mounting example in which the same semiconductorsubstrate 80 as that shown as the semiconductor chip in FIG. 32 ismounted on the header portion 169 a of another lead frame 169 in thereal space. The mounting example takes out only two output signals inplace of four output signals from the semiconductor substrate 80.

The lead frame 169 includes a lead pin 169 b for grounding continuedintegrally with the header portion 169 a, a lead pin 169 c to which thepower voltage is supplied, and two lead pins 169 d and 169 e for signaloutput. The lead pins 169 b, 169 c, 169 d and 169 e are connected to thecorresponding terminals (bonding pads) GND, VCC, VOB1 and VOB2 via Auwires 199 b, 199 c, 199 d and 199 e, respectively.

By virtue of the layout on the surface of the semiconductor substrate 80and, in particular, the terminals GND, VCC, VOB1 and VOB2 arranged alongthe peripheral portion of the semiconductor substrate 80, products ofdifferent types can be manufactured in spite of employing the samesemiconductor substrate 80.

When the output signal formed by the logic circuit section 86 is takenout of the semiconductor substrate 80, it is sometimes the case wherethe amount of current is increased to make the output signal have lowimpedance. In such a case, the voltage change becomes large when theoutput signal changes between high level and low level. Therefore, it isconcerned that such a voltage change is fed back to the input of thelogic circuit section 86 and sometimes causes malfunction. In such acase, it is desirable to provide a delay section that delays the outputsignal formed by the logic circuit section 86 with respect to the signalinputted to the logic circuit section 86, and this prevents theoccurrence of malfunction. Such a delay section is well known andconstituted by introducing a capacitance or the like (not shown).However, it is necessary to adjust the capacitance value in conformityto the frequency used.

Moreover, although the constant current is supplied as the base currentto the transistors of the amplification circuits OC1, OC2, OC3 and OC4that constitute the output circuit section 87 in the example of FIG. 23,the present invention is not limited to this. For example, theamplification circuit OC shown in FIG. 34 has a pre-stage npn transistor871 that receives the signal from the exclusive-OR circuit at its baseand amplifies the same, and a post-stage npn transistor 872 thatreceives the output of the transistor 871 at its base and amplifies thesame. The base of the post-stage npn transistor 872 is connected to thepower source Vcc via a resistor 873. That is, the base current of thetransistor 872 is a power voltage dependence current. When the basecurrent is the power voltage dependence type as described above, acapability to extract the current is improved. Therefore, themalfunction of the output circuit section 87 and, consequently, thephotoelectric encoder are suppressed even when electric charge isaccumulated by the turbulence of static electricity or the like.

In the electronic equipment provided with the photoelectric encoder, thephotoelectric encoder detects the passing of the slits X1, X2, . . . andthe light-off portions Y1, Y2, . . . of the moving object 40 with highaccuracy. Therefore, appropriate operation can be carried out by usingthe detection results.

Although the photoelectric encoder of the light transmission type hasbeen described in the present embodiment, the present invention is, ofcourse, not limited to it. The present invention is similarly applied tothe photoelectric encoder of the light reflection type. It is noted thatthe slits of the moving object correspond to the light-off portion thatmakes no light be incident on the light-receiving devices, and theportions constructed of the plate member (portions that reflects light)located between the slits correspond to the light-on portion that makeslight be incident on the light-receiving devices in the light reflectiontype conversely to the light transmission type, as already described.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A photoelectric encoder comprising: a light-emitting device; and aplurality of light-receiving devices arranged in one direction in aregion that light from the light-emitting device can reach, fordetecting an amount of movement of a moving object, the moving objectalternately having in a common pitch a light-on portion that produces astate in which light is incident from the light-emitting device to thelight-receiving devices and a light-off portion that produces a state inwhich the light is not incident from the light-emitting device to thelight-receiving devices, wherein the plurality of light-receivingdevices have same dimensions and comprise a first group of fourlight-receiving devices which are arranged in the one direction in asecond pitch such that phases of the four light-receiving devices in thefirst group are different from each other by 45° in a light-on portionwidth and a second group of four light-receiving devices which arearranged in a third pitch such that phases of the four light-receivingdevices in the second group are different from each other by 45° in alight-off portion width, the second group of four light-receivingdevices corresponding with the first group of four light-receivingdevices; and a comparing section which respectively obtains first,second, third and fourth differential signals by taking a differencebetween outputs of light-receiving device pairs, each light-receivingdevice pair having a first light-receiving device from the first groupof light-receiving devices and a second light-receiving device from thesecond group of light-receiving devices, of which phases of the pairedoutputs are different from each other by 180°; a first logical operatingsection which takes an exclusive-OR of logical values expressed by thefirst and second differential signals that have phases different fromeach other by 90°; and a second logical operating section which takes anexclusive-OR of logical values expressed by the third and fourthdifferential signals that have phases different from each other by 90°,wherein the comparing section comprises a plurality of amplifierscorresponding to the respective light-receiving device pairs, theplurality of amplifiers are arranged in the one direction along an arrayconstructed of the plurality of light-receiving devices, and a centerposition of the array constructed of the plurality of light-receivingdevices and a center position of an array constructed of the pluralityof amplifiers coincide with each other in the one direction.
 2. Thephotoelectric encoder as claimed in claim 1, further comprising: aplurality of identical supply current circuits, each for supplying acurrent to one of the amplifiers.
 3. The photoelectric encoder asclaimed in claim 1, wherein the plurality of amplifiers are arranged ina center portion of a semiconductor substrate on which the plurality oflight-receiving devices are arranged in common.
 4. The photoelectricencoder as claimed in claim 1, wherein among the plurality ofamplifiers, amplifiers arranged adjacent to each other make a pair ofamplifiers, and logical values each of which is expressed by thedifferential signal outputted from the pair of amplifiers are subjectedto operation by the first or second logical operating section. 5.Electronic equipment comprising the photoelectric encoder claimed inclaim 1.